2d Basin Modelling in the Eastern Variscan Fold Belt (Czech Republic): Influence of Thrusting on Patterns of Thermal Maturation

Abstract

This study evaluates the geothermal history of Palaeozoic sedimentary rocks from the easternmost part of the Variscan external zone in the NE Czech Republic. The objective was to investigate the geothermal history of pre‐Variscan Palaeozoic carbonates in the study area, and to assess its relationship with that of the overlying Variscan flysch. In the study area, the Palaeozoic succession occurs at the surface or is overlain by Miocene sediments of the Carpathian Foredeep. Palaeozoic nappes and the main Variscan overthrust have been documented in the subsurface at the deep Potštát‐1borehole. Vitrinite reflectance measurements on 38 samples from the Potštát‐1 well and 19 samples from nearby surface outcrops and shallow boreholes were available. A 2D thermal model was created using PetroMod and the thermal maturity evolution was modelled by EASY%Ro. The thermal model was constructed based on interpretations of two NW‐SE seismic profiles (lines 5/83 and 5/84) oriented perpendicular to the main Variscan thrusts. The results were calibrated using measured vitrinite reflectance and were adjusted with 1D models from three shallow boreholes. At the Potštát‐1 borehole, modelled maximum palaeo‐temperatures of the Variscan flysch (Moravice Formation) ranged from 310°C at a depth of 7.3 km (the top of the preserved succession) to 395°C at the base of the succession, resulting in thermal maturities of >4%Rr. Peak maturation occurred prior to the end of Variscan thrusting. Modelling suggests that the basal heat flow for these thrust units reached a maximum value of 63 mW/m2 at 325 Ma. In addition, the modelling suggests that the maturity of the Palaeozoic carbonates was controlled by the thickness of the overlying Variscan flysch nappes. Maximum palaeo‐temperatures for the Palaeozoic carbonates ranged from 265°C at the top of the interval (at a depth of 7.1 km) to 290°C at the base, resulting in a maturity of 3.8 to >4%Rr which is within the dry gas window. The study suggests that basal heat flows in the original (pre‐thrust) Early Carboniferous sedimentary basin were slightly higher than those in the post‐thrust location for the Variscan flysch nappes. This should be taken into account when evaluating the petroleum system in the South Moravian oil province (SW Czech Republic) where a complete sedimentary sequence has not been preserved.

Charging history and fluid evolution for the Carboniferous volcanic reservoirs in the western Chepaizi Uplift of Junggar Basin as determined by fluid inclusions and basin modelling

“…The boundary conditions such as paleo‐water depth (PWD), sediment–water interface temperature (SWIT), and basal heat flow (HF) must be defined throughout the simulated geologic history. The HF is the most important boundary condition and allows the maturity of potential source rocks to be predicted (Jirman, Geršlová, Kalvoda, & Melichar, ).…”

“…Wang et al (, 2007), and they summarized PWD parameters of various sedimentary facies and concluded the changes of PWD within 0 to 30 m in the western Chepaizi Uplift because of the long‐term paleo‐high (Table ). User‐defined lithological compositions (Table ) assigned to individual layers were based on descriptions of drill cuttings and cores from wells P70 and Su2 (Jirman et al, ).…”

Tectono-thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: a case study of Jebel Akhdar, Oman

“…Time-temperature histories were reconstructed using the HeFTy 1.8.3 software package (Ketcham, 2005) applying the kinetic zircon properties of Guenther et al (2013). For samples with reset zircons the only constraint used was a minimum temperature above 200 • C between deposition and the calculated ZHe age.…”

Source rock potential of the Miocene sedimentary rocks in the Carpathian Foredeep of the Czech Republic

“…Lo cal and re gional un con formi ties within the Mio cene succes sion are de vel oped due to the vary ing in ten sity and ori en tation of flex ural load ing and dif fer ent in her ited geo log i cal and tectonic base ment struc ture, as well as due to the polyphase nature of the ac tive ba sin mar gin and a grad ual change in its po sition (Brzobohatý and Cicha, 1993;Eliáš and Pálenský, 1998;Nehyba and Petrová, 2000;Krzywiec, 2001;Kováè et al, 2003Kováè et al, , 2004Oszczypko et al, 2006;Nehyba and Šikula, 2007;Francírek and Nehyba, 2016). Seis mic and bore hole data show that the bed rock in the area stud ied con sists of Pro tero zoic crys tal line rocks of Brunovistulicum, De vo nian to Lower Car bon if er ous car bon ates, and Car bon if er ous siliciclastic de pos its -"Culm fa cies" of the Moravian-Silesian Pa leo zoic (Jirman et al, 2018). Ero sional rel ics of Ju ras sic and autochthonous Paleogene strata are also pres ent, es pe cially in the south ern seg ment of the area analysed (Fig.…”